Commercial two-component epoxy systems are packaged in a dual cartridge system, which dispenses an appropriate amount of curable epoxy resin and an epoxy curing agent. The dispensed curable epoxy resin and curing agent are then mixed to contact and react the curing agent with the curable epoxy resin, which then cures.
To obtain the maximum performance characteristics of the epoxy system, it is important that the curable epoxy resin and curing agent are adequately mixed and cured.
Because the colors and viscosities of the curable epoxy resin and the curing agent are often similar, it may be difficult to detect the completeness of mixing. Furthermore, after mixing, the epoxy system can be handled (e.g., poured and worked) until gelation occurs. Therefore, it is also useful to know when the epoxy system has sufficiently cured.
Traditionally, a single dye has been added to either the curable epoxy resin or the curing agent to indicate complete mixing and/or curing. For example, U.S. Pat. No. 3,773,706 (Dunn) describes adding phenosafranin dye to a curable epoxy system to indicate cure. Great Britain Pat. No. 927,541 describes adding a triphenylmethane or anthraquinone dye to the curable epoxy resin to indicate complete mixing based on the uniformity of color, which changes color again upon gelation. U.S. Pat. No. 4,160,064 (Hodiff et al.) describes adding a coloring agent to the curable epoxy resin to impart a latently transient color to assist in determination of complete mixing, which becomes essentially colorless upon the curing of the mixture.